1. Field of the Invention
The present invention relates generally to an image forming machine and, more particularly, to a system and method for monitoring media stack height in an image forming machine and a method of calibrating stack height sensing in the media stack height monitoring system.
2. Description of the Related Art
As a whole, image forming devices, such as inkjet printers, that feed sheets of media from a stack are deficient in their means to provide a warning of an impending depleted stack condition. As a consequence, if a user sends a job to such a device without knowing if there are a sufficient number of sheets in the stack for its completion, and if the stack depletes during the print job, the user will have to reload the stack and restart, causing a delay in the job's completion. With the proliferation of network inkjet printers, the ability to make a visual assessment of stack level is reduced, and the delays caused by unexpected stack depletions are more frequent and longer in duration.
U.S. Pat. No. 7,374,163, assigned to the assignee of the present invention, discloses a media stack height sensing mechanism in an image forming device which employs a pivotally mounted arm that is in contact with the top of a media stack. A flag attached to the arm is characterized by varying transmissivity. The flag is moveable with the arm so that as the position of the arm changes in relation to the stack height, a different portion of the flag is positioned between a transmitter and receiver of an optical sensing mechanism disposed within the image forming device. The flag accordingly reduces the amount of optical energy received by the receiver. The receiver output signal indicates the height of the media stack. The flag also includes features that further limit light transmission to the receiver to provide discrete stack height indications such as low, empty, full, or intermediate states. However, the addition of yet another single-function component to all image forming devices, like the media stack height sensor of the cited patent, is an additional benefit not justified by its added cost across the board for all image forming devices.
Thus, there is still a need for an innovation that can give a user an indication of the present stack height so that the user may adjust the stack load or the job format to ensure uninterrupted completion.